1. Field of the Invention
The present invention relates to a bumper reinforcement. In particular, the present invention relates to a bumper reinforcement in the front or rear of the body of an automobile to resist to collision impact during a vehicle collision.
2. Description of Related Art
An automobile may typically be provided with a bumper structure in the front or rear of the automobile body to receive an impact caused by a vehicle collision. The bumper structure generally includes a core member called a bumper reinforcement. The bumper reinforcement is disposed in the automobile body to extend along the width of the automobile body, and supported at its end sections by support members that are attached to the body frame of the automobile.
FIG. 12 schematically illustrates a conventional bumper reinforcement 114. The bumper reinforcement 114 is generally composed of a body member 120 and a closure member 122. The body member 120 has an inverted hat-shaped cross section as seen in FIG. 12, with an open side upward, and flanges 126 extending outward from the open side edges. The opening of the body member 120 is closed by the closure member 122 so that the bumper reinforcement 114 has a closed cross section. The closure member 122 is spot welded at 128 to the flanges 126 of the body member 120.
In the bumper reinforcement 114 shown in FIG. 12, the upper surface of the closure member 122 provides an impact surface during a vehicle collision as seen in FIG. 12, expecting that a collision impact may input the bumper reinforcement 114 from above during a vehicle collision. The performance of the bumper reinforcement 114 during such a vehicle collision can be evaluated under a three-point bending test as illustrated in FIG. 13. In the three-point bending test, the bumper reinforcement 114 is supported by support members 118 positioned where bumper support structures would be situated, and then an impact load is applied to the center of the upper surface with a loading means 136, also called an impactor.
When subjected to an impact load by the impactor 136, the bumper reinforcement 114 bear the load with its middle section deflected downward as indicated by the dashed line in FIG. 13. The bumper reinforcement 114 has a closed cross section to provide a higher strength so that the bumper reinforcement can bear greater impact load.
As the bumper reinforcement 114 is deflected downward under the impact load as shown in FIG. 13, the welding, joints between the flanges 126 of the body member 120 and the closure member 122 will experience forces directed such as to exfoliate the welded joints, as indicated by the arrows in FIG. 12. This is because the welded surfaces extend perpendicular to the direction of the applied load.
As generally known, a joint by spot welding has a lower strength against exfoliation than against shearing. The conventional cross-sectional configuration as described above may lead to exfoliation of the spot welds between the flanges 126 of the body member 120 and the closure member 122, and thus the closed cross section of the bumper reinforcement may not sufficiently demonstrate its effect in strength.
In addition, the conventional bumper reinforcement 114 in which the closure member 122 serves as an impact surface as described above may result in a inward deflection or collapse of the sidewall portions 120b and 120c of the body member 120, and therefore cannot provide a sufficient strength.